Summary translation

A cross-sectional study was carried out to estimate the prevalence of gastrointestinal helminths on Swedish laying hen farms with different housing systems, and to identify associated risk factors. The study population consisted of laying hens housed in conventional or enriched cages, single-tiered floor systems, multi-tiered aviary systems, free-range and organic production. Pooled faecal samples were obtained from laying hens on 202 farms representing approximately 60% of the Swedish laying hen farms. Data on rearing conditions of pullets, production characteristics, biosecurity level, and presence of other poultry and wild birds on the farms were collected. Parasite identification to species level was made from 16 randomly selected parasite infected flocks. Additionally, pooled faecal samples for parasitologic analysis were collected from pullet flocks (n=36). Based on the assumption that the epidemiology of Ascaridia spp. and Heterakis spp. is similar (both have simple direct life-cycles and the parasite ova require at least ten to 14 days to each the infective stage) each investigated risk factor was analyzed using a logistic regression model. Nematode eggs (Ascaridia spp. or Heterakis spp.) were detected from one of the 36 pullet flocks of which the majority had been reared in non-cage systems. One of 44 laying hen flocks housed in cages was infected (2%). Nematode eggs were detected in 21 of 78 flocks housed in single-tiered floor system (27%), in 6 of 39 flocks from multi-tiered aviary systems (15%), and in 45% of the flocks with access to outdoor pens or pasture (organic flocks and free-range systems). Parasites were identified at necropsy from the 16 randomly selected laying hen flocks from which nematode eggs hade previously been detected. Ascaridia galli were found in 11/16 flocks and Heterakis gallinarum in 9/16 flocks. Organic hen flocks were often infected by both species. The most significant risk factor for nematodiasis (Ascaridia spp., Heterakis spp. and/or Capillaria spp.) was housing system. Free-range and organic hens were at higher risk of infection than caged layers (OR=30, 95% CI 2.6-358). Absence of a hygiene barrier at the entrance of the house or unit was another risk factor (OR 7.9, 95% CI 2.4-26). The risk of nematodiasis increased with time elapsed since the change of housing equipment (OR=4.5, 95% CI 1.3-15) for a 10-year-old house compared with a new house. Factors that were not associated with infection included hybrid, number of units on farms and housing systems on the farms, and presence of other poultry, bird ponds or wild birds on the farms. Our analysis indicated that efficient biosecurity measures on table-egg producing farms protect the birds from nematodiasis. In our analysis, pullets did not appear to be source of nematodes. However, the number of tested pullet flocks was small and the birds may have been too recently infected to shed parasite ova. Contacts between farms in combination with a change in housing systems for laying hens appeared to be associated with the recent reoccurrence in Sweden of nematodiasis.